Descaling device and method for chemically descaling a metal strip

ABSTRACT

A descaling device ( 2 ) for chemically descaling a metal strip ( 4 ): A spraying device ( 12, 12   a - 12   d ) for spraying a pickling agent ( 14 ) onto a top or bottom side ( 16, 18 ) of the metal strip ( 4 ). The spraying device ( 12, 12   a - 12   d ) has a first outer spraying unit ( 50 ) for spraying the pickling agent ( 14 ) onto a first edge region ( 52 ) of the top/bottom side ( 16, 18 ) of the metal strip ( 4 ) and a second outer spraying unit ( 54 ) for spraying the pickling agent ( 14 ) onto a second edge region ( 56 ) of the top/bottom side ( 16, 18 ) of the metal strip ( 4 ), which second edge region lies opposite the first edge region ( 52 ). At least one of the two outer spraying units ( 50, 54 ) has one or more solid stream nozzles ( 20 ), in particular a plurality of rows of solid stream nozzles ( 20 ), and/or one or more slotted nozzles ( 22 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. §§ 371 national phase conversionof PCT/EP2018/058305, filed Mar. 30, 2018, the contents of which areincorporated herein by reference which claims priority of EuropeanPatent Application No. 17164759.7, filed Apr. 4, 2017, the contents ofwhich are incorporated by reference herein. The PCT InternationalApplication was published in the German language.

The invention relates to a descaling device for the chemical descalingof a metal strip and to a method for chemical descaling of a metalstrip.

TECHNICAL BACKGROUND

During hot rolling of a metal strip, a scale layer forms on its surface.Prior to any subsequent cold rolling of the metal strip, the scale layermust be removed. Especially for this reason, after hot rolling, a metalstrip is usually subjected to a descaling, during which the scale layeris removed.

In the field of chemical descaling of a metal strip, where anacid-containing pickling agent is usually used, one distinguishesbetween so-called dip pickling and so-called spray pickling. In dippickling, the metal strip being treated is dipped into a dip tank filledwith the pickling agent, whereas in spray pickling the pickling agent issprayed onto the metal strip being treated. The spray picklingtechnology is characterized by a shorter treatment time as compared todip pickling.

The problem which the invention proposes to solve is to enable a highpickling effectiveness to be achieved in a pickling spray treatment of ametal strip.

This problem is solved according to the invention by a descaling deviceand by a method according to the invention.

The descaling device according to the invention for the chemicaldescaling of a metal strip comprises at least one first spraying deviceand at least one further spraying device for respectively spraying apickling agent onto a top side or bottom side of the metal strip. Thefirst spraying device and the further spraying device comprise a firstouter spraying unit for spraying the pickling agent onto a first edgeregion of the top side/bottom side of the metal strip and a second outerspraying unit for spraying the pickling agent onto a second edge regionof the top side/bottom side of the metal strip situated opposite thefirst edge region. Furthermore, the first spraying device furthercomprises a middle spraying unit for spraying the pickling agent onto amiddle region of the top side/bottom side of the metal strip situatedbetween the edge regions.

At least one of the two outer or the middle spraying units of the firstspraying device comprises multiple rows of solid stream nozzles and eachof the spraying units of the first spraying device comprises its ownpickling agent distribution chamber.

At least one of the two outer spraying units of the further sprayingdevice comprises one or more slotted nozzles and each of the two outerspraying units has its own pickling agent distribution chamber.

The nozzles of the respective spraying units are advantageouslyconnected to their pickling agent distribution chamber. Such anembodiment of the spraying device enables an easily manufacturedconstruction of the spraying device as well as slight control expensefor the spraying device.

Solid stream nozzles are relatively robust and easy to manufacture onaccount of their simple geometry.

Whereas nozzles used heretofore in descaling devices, such as flatstream nozzles, tongue nozzles, or conical jet nozzles, each produce ajet which expands and therefore has an inhomogeneous momentumdistribution, with the aid of a solid-stream nozzle one can create aclosed, stable and high-energy solid stream, having a homogeneousmomentum distribution across its jet diameter and expanding little if atall over a long distance. With such a high-energy solid stream, thelaminar boundary layer of the pickling agent formed or forming on themetal strip can be kept as thin as possible, having a positive impact onthe material exchange and thus enhancing the pickling effectiveness.Furthermore, such a high-energy solid stream makes it possible to “washaway” clinging scale.

Due to the higher pickling effectiveness, the necessary treatment timefor complete descaling of the metal strip can be shortened. This makespossible a shorter treatment lane (shorter structural length) or, forthe same treatment lane, a higher delivery speed of the metal strip.

Furthermore, when using one or more solid stream nozzles for thespraying device, a lower pickling agent supply pressure is required thanwhen using flat stream nozzles, tongue nozzles, or conical jet nozzlesin order to achieve the same effect, because the jet of a solid-streamnozzle expands little if at all over a long distance and thus makes ahigh impact action on the metal strip surface possible. This, in turn,makes lower operating costs possible, e.g., because more favorable pumpscan be used. For example, the spraying devices can be operated with apickling agent supply pressure of 4 bar.

Moreover, the jet produced by a solid-stream nozzle advantageouslycontains no admixture of surrounding air. In other words, the jet whichis produced by a solid-stream nozzle advantageously does not mix withthe surrounding air.

The solid stream nozzles of the spraying device preferably each have apickling agent outlet bore with nonconstant cross section. Thus, forexample, the cross section area of the pickling agent outlet bore of therespective solid-stream nozzle may decrease toward the outlet-sidenozzle end of the solid-stream nozzle. By the outlet-side nozzle end ofa nozzle is meant its end facing the metal strip. Accordingly, by theinlet-side nozzle end of a nozzle is meant its end facing away from themetal strip.

Preferably, the narrowest point of the pickling agent outlet bore of therespective solid-stream nozzle is located at its outlet-side nozzle end.The pickling agent outlet bore of the respective solid-stream nozzle maybe configured as a funnel, in particular.

Moreover, preferably the pickling agent outlet bore of the respectivesolid stream nozzle has at its narrowest place an inner diameter of atleast 2 mm and at most 6 mm. Especially preferably, the pickling agentoutlet bore of the respective solid stream nozzle has at its narrowestplace an inner diameter of 4 mm.

One modification of the descaling device according to the inventioncalls for the further spraying device to comprise in addition a middlespraying unit with one or more slotted nozzles for spraying the picklingagent onto a middle region of the top side/bottom side of the metalstrip situated between the edge regions, as well as its own picklingagent distribution chamber.

While a pickling agent jet produced by a solid-stream nozzle typicallyresults in a pointlike application of pickling agent to the metal stripsurface, a pickling agent jet produced by a slotted nozzle usuallyresults in a linear application of pickling agent to the metal stripsurface. With the aid of a slotted nozzle, a closed, stable andhigh-energy jet can be created, having a homogeneous momentumdistribution and expanding little if at all over a long distance. Thanksto the use of one or more slotted nozzles, similar results can beachieved as in the use of one or more solid stream nozzles.

Advantageously, the descaling device comprises a strip conveying devicefor transporting the metal strip along a horizontal conveying direction.The strip conveying device may be designed, e.g., as a roller conveyor.Preferably, the conveying direction corresponds to the length directionof the metal strip being treated. In other words, the metal strip ispreferably transported by the strip conveying device along its lengthdirection.

Preferably, the two outer spraying units are outfitted with nozzles ofthe same type. If the first outer spraying unit for example has one ormore solid stream nozzles, then the second outer spraying unit willpreferably likewise have one or more solid stream nozzles. If the firstouter spraying unit has one or more slotted nozzles, then the secondouter spraying unit will preferably likewise have one or more slottednozzles.

Moreover, it is advantageous for the spraying device to have a middlespraying unit for spraying the pickling agent onto a middle region ofthe top side/bottom side of the metal strip situated between the edgeregions. It is especially preferable for the middle spraying unit tocomprise one or more solid stream nozzles, especially multiple rows ofsolid stream nozzles, and/or one or more slotted nozzles, especially forthe aforementioned reasons.

Each of the aforementioned spraying units advantageously comprises agroup of nozzles for spraying the pickling agent onto the topside/bottom side of the metal strip.

Advantageously, the spraying device is designed as a spray bar. In thiscase, the aforementioned pickling agent distribution chambers may beformed for example with the aid of partition walls arranged inside thespray bar, especially metal dividers. In other words, in the case of anembodiment of the spraying device as a spray bar, the individualpickling agent distribution chambers may be separated from each other bymultiple partition walls, especially metal dividers. The partition wallsadvantageously cause only a slight decrease in the internal volume ofthe spray bar, so that friction losses inside the spray bar can be keptlow.

In another variant of the invention, the spraying device may comprisefor example separate spray bars, forming the aforementioned sprayingunits. In such a case it is advisable for these separate spray bars tobe arranged with an offset from each other perpendicular to theconveying direction. They may likewise be arranged with an offset fromeach other in the conveying direction. Alternatively, the separate spraybars may be arranged in the same position relative to the conveyingdirection.

Moreover, the spraying device may comprise a device in each of itspickling agent distribution chambers ensuring that the pickling agent isapplied homogeneously to the nozzles of the respective spraying unit.

Preferably, the spraying device has an interior height of at least 10cm. This makes it possible to avoid high pressure gradients inside thespraying device. By the interior height of the spraying device is meantits inner dimension perpendicular to the top side/bottom side of themetal strip.

The descaling device may have a pickling agent supply line for each ofthe three spraying units. Advantageously, the descaling device comprisesa first pickling agent supply line, which is connected at the outletside to the first outer spraying unit, a second pickling agent supplyline which is connected at the outlet side to the second outer sprayingunit, and a third pickling agent supply line which is connected at theoutlet side to the middle spraying unit.

Advantageously, each of the three pickling agent supply lines emptiesinto the respective spraying unit perpendicular to its sprayingdirection. That is, advantageously the first pickling agent supply lineempties perpendicular to the spraying direction of the first outerspraying unit into the first outer spraying unit, while the secondpickling agent supply line empties perpendicular to the sprayingdirection of the second outer spraying unit into the second outerspraying unit and the third pickling agent supply line emptiesperpendicular to the spraying direction of the middle spraying unit intothe middle spraying unit. In this way, a uniform pressure distributioncan be achieved in the individual spraying units and thus a uniformpressure distribution at their nozzles.

Each of the spraying units is advantageously adapted to spraying thepickling agent in perpendicular or substantially perpendicular manneronto the top side/bottom side of the metal strip. This is accomplished,e.g., if the nozzles of the spraying units are oriented such that thespraying units each time have a spraying direction which is orientedperpendicular or substantially perpendicular to the top side/bottom sideof the metal strip, i.e., vertically or substantially vertically upwardor vertically or substantially vertically downward.

By the spraying direction of the respective spraying unit is meant thedirection in which the spraying unit sprays out the pickling agent. Thephrasing “substantially perpendicular to the top side/bottom side of themetal strip” may be understood as having a deviation of up to +/−20°,preferably up to +/−10°, from the right angle to the top side/bottomside of the metal strip.

Furthermore, at least one of the spraying units of the spraying devicemay be tilt or swivel-mounted, preferably about a horizontal axis,parallel to the conveying direction.

In one advantageous embodiment of the invention, the descaling devicecomprises a control device by means of which a pickling agent dispersingrate of the respective spraying unit of the spraying device isadjustable, especially continuously or in several discrete steps.

The pickling agent dispersing rate of the respective spraying unit isunderstood to be the quantity of pickling agent emerging from therespective spraying unit per unit of time, in other words the volumeflow of the pickling agent emerging from the respective spraying unit.

In the sense of the invention, controlling a quantity may includeregulating that quantity, i.e., a control with a measured valuefeedback. The aforementioned control device may thus be in particular aregulating device.

Moreover, in the sense of the invention a quantity is “adjustable inseveral discrete steps” if that quantity can also be set at anothervalue between a value other than zero and a maximum value of thequantity (which can be achieved in the descaling device). In otherwords, in the sense of the invention, a quantity is “adjustable inseveral discrete steps” if that quantity can be set at least at twovalues other than zero.

By means of the control device, the pickling agent dispersing rate ofthe middle spraying unit is preferably adjustable independently of thepickling agent dispersing rate of the first outer spraying unit andindependently of the pickling agent dispersing rate of the second outerspraying unit. This makes it possible to adjust the pickling agentapplication to the metal strip in the width direction according to thenature of the width profile of the thickness of the scale layer on thetop side/bottom side of the metal strip.

Typically, the thickness of the scale layer at the strip edges isgreater than in the strip middle region. If the metal strip is appliedwith pickling agent homogeneously over its width, this will have theeffect of “overwetting” the strip middle region in the event of a heavypickling agent application, i.e., not only the scale layer but also basematerial lying underneath will also be removed by the pickling agent,whereas in the event of a slight pickling agent application the scalelayer will not be entirely removed, especially at the strip edges.

If the metal strip has a greater thickness of the scale layer at theedge regions of its top side/bottom side than in the middle region ofthe top side/bottom side situated in between them, the pickling agentdispersing rate of the middle spraying unit can be set at a lower valuethan the pickling agent dispersing rate of the outer spraying units. Inthis way, it is possible to achieve a homogeneous descaling result.Since an overpickling of the metal strip can be avoided in this way, itis furthermore possible to reduce the need for pickling agent, which inturn makes possible a decrease in the cost of regeneration of thepickling solution.

Preferably, the pickling agent dispersing rate of the first outerspraying unit is adjustable by means of the control device independentlyof the pickling agent dispersing rate of the second outer spraying unit.In this way, it is possible to apply a different amount of picklingagent to the first edge region of the top side/bottom side of the metalstrip than to the second edge region of the top side/bottom side of themetal strip.

Further, the control device may comprise multiple pickling agentdelivery pumps connected at the exit side to the spraying device. Withthe aid of the pickling agent delivery pumps, the pickling agent can bedelivered to the spraying device. The pickling agent delivery pumps canbe used to adjust the pickling agent dispersing rates of the sprayingunits. In particular, the pickling agent delivery pumps may befrequency-regulated pumps.

One of the pickling agent delivery pumps may be connected to the twoouter spraying units, while another of the pickling agent delivery pumpscan be connected to the middle spraying unit. Alternatively, a firstpickling agent delivery pump can be connected to the first outerspraying unit, a second pickling agent delivery pump to the second outerspraying unit and a third pickling agent delivery pump to the middlespraying unit.

The pickling agent delivery pumps are preferably connected to a controlunit of the control device. The control unit is advantageously designedto adjust the delivery performance of the respective pickling agentdelivery pump, especially continuously or in several discrete steps.Further, it is advantageous for the delivery performance of therespective pumps to be adjustable independently of the deliveryperformances of the other pickling agent delivery pumps. By altering therespective delivery performance, the pickling agent dispersing rate ofthe respective spraying unit can be altered.

Furthermore, the control device may comprise multiple valves. These maybe used alternatively or additionally to the pickling agent deliverypumps for adjusting the pickling agent dispersing rates of the sprayingunits. Advantageously, the spraying device is connected at the entryside to the valves, especially across the aforementioned pickling agentsupply lines.

For the two outer spraying units, a common valve or a respectiveseparate valve each may be provided. The middle spraying unit ispreferably provided with its own valve. Further, it is advantageous forthe valves to be connected to the control unit of the control device.

The control unit is preferably designed to adjust the valve position ofthe respective valve, especially continuously or in several discretesteps. By altering the respective valve position, the pickling agentdispersing rate of the respective spraying unit can be altered.

Moreover, the aforementioned pickling agent supply lines may berespectively outfitted with a pressure and/or flow rate sensor formonitoring the pickling agent pressure or the pickling agent flow ratein the respective pickling agent supply line. These sensors arepreferably connected to the control unit of the control device. Thecontrol device, especially its control unit, may be designed to controlthe aforementioned pickling agent delivery pumps and/or the valves independence on the sensor signals of these sensors.

In addition to the aforementioned spraying units, the spraying devicemay comprise further spraying units for spraying the pickling agent ontothe top side/bottom side of the metal strip. For example, the sprayingdevice may comprise between the middle and the first outer spraying unita first further spraying unit and between the middle and the secondouter spraying unit a second further spraying unit. The pickling agentdispersing rate of the respective further spraying unit is preferablyadjustable by means of the control device independently of the picklingagent dispersing rates of the other spraying units of the sprayingdevice.

Furthermore, the control device may comprise a sensor unit having one ormore sensors for detecting a surface parameter of the metal strip,especially a surface parameter dependent on a thickness of the scalelayer of the metal strip.

The surface parameter can be, for example, the thickness of the scalelayer itself or another surface parameter dependent on the thickness ofthe scale layer. In particular, the sensor unit may comprise one or morenoncontact measuring sensors for detecting the surface parameter.

Moreover, the sensor unit may be designed in particular to measure saidsurface parameter with position resolution across the width of the metalstrip, in other words a width profile of the surface parameter. Thesensor unit may be arranged before or after the spraying device in termsof the conveying direction.

Furthermore, it is advantageous for the sensor unit to be connected tothe control unit of the control device. The control device, especiallyits control unit, is designed to adjust the pickling agent dispersingrate of the respective spraying unit in dependence on an output signalof the sensor unit.

Furthermore, the pickling agent dispersing rate of the respectivespraying unit can be controlled in dependence on one or more knownproduction parameters, such as the so-called coiling temperature of themetal strip and/or its material grade. Such a parameter isadvantageously relayed to the control device, especially to its controlunit. Preferably, the control unit is designed to calculate the picklingagent dispersing rate to be set for the respective spraying unit withthe aid of the sensor signals and/or production parameters relayed tothe control unit.

Furthermore, the descaling device may comprise at least one further orsecond spraying device, especially at least one further spray bar, forspraying the pickling agent on the same side of the metal strip as thefirst mentioned spraying device. The first mentioned and the furtherspraying device(s) are preferably arranged in succession in theconveying direction.

Just like the first mentioned spraying device, such a further sprayingdevice may comprise a first outer spraying unit for spraying thepickling agent onto the first edge region of the top side/bottom side ofthe metal strip and a second spraying unit for spraying the picklingagent onto a second edge region of the top side/bottom side of the metalstrip. Optionally, such a further spraying device may comprise a middlespraying unit for spraying the pickling agent onto the middle region ofthe top side/bottom side of the metal strip. Preferably, in such afurther spraying device the pickling agent dispersing rates of itsspraying units can be controlled by means of the control device in thesame way as the pickling agent dispersing rates of the spraying units ofthe first mentioned spraying device.

Moreover, the first mentioned and the further spraying device(s) mayhave different kinds of nozzles. One of the spraying devices may have,e.g., solid stream nozzles (exclusively), another of the sprayingdevices may in turn have, e.g., slotted nozzles (exclusively).

Furthermore, the descaling device may comprise at least one additionalspraying device for spraying the pickling agent on the other side of themetal strip. The phrasing “other side” of the metal strip should beunderstood here as meaning that if the first mentioned spraying devicesprays the pickling agent onto the top side of the metal strip, then theother side is the bottom side of the metal strip. Conversely, if thefirst mentioned spraying device sprays the pickling agent onto thebottom side of the metal strip, then the other side is the top side ofthe metal strip. The features mentioned in connection with the firstmentioned spraying device may pertain in analogous manner to such anadditional spraying device.

Those elements of the descaling device which come into contact with thepickling agent advantageously consist of an acidresistant material,especially a plastic and/or a ceramic. The aforementioned nozzles mayfor example consist of polyvinylidene fluoride (PVDF) and/orpolypropylene (PP), or contain these materials.

Furthermore, the descaling device may comprise a dip tank for a dippickling treatment of the metal strip. This is preferably arranged afterthe spraying device in terms of the conveying direction. The dippickling treatment in the dip tank may serve to even out the picklingeffect and/or to remove scale residue not removed during the spraytreatment.

Moreover, the descaling device may comprise a further dip tank for a dippickling treatment of the metal strip, the spraying device beingarranged between the two dip tanks in terms of the conveying direction,for example.

In the method according to the invention for the chemical descaling of ametal strip, a pickling agent is sprayed onto a top side or bottom sideof the metal strip by means of at least one first spraying device and atleast one further or second spraying device. In this process, thepickling agent is sprayed by a first outer spraying unit of the firstand the further spraying device onto a first edge region of the topside/bottom side of the metal strip and by a second outer spraying unitof the first and the further spraying device onto a second edge regionof the top side/bottom side of the metal strip situated opposite thefirst edge region. In addition, a pickling agent is sprayed by a middlespraying unit of the first spraying device onto a middle region of thetop side/bottom side of the metal strip situated between the edgeregions. In the method according to the invention it is provided thatthe pickling agent is sprayed onto the top side/bottom side of the metalstrip by at least one of the two outer spraying units or the middlespraying unit of the first spraying device through multiple rows ofsolid stream nozzles and by at least one of the two outer spraying unitsof the further spraying device through one or more slotted nozzles.

It is especially preferable when the pickling agent is sprayed onto amiddle region of the top side/bottom side of the metal strip situatedbetween the two edge regions through one or more slotted nozzles of amiddle spraying unit of the at least one further spraying device.

The descaling device according to the invention may be used to carry outthe method according to the invention. That is, the devices mentioned inconnection with the method may be in particular elements of thedescaling device.

The spraying of the pickling agent onto the metal strip preferablybrings about not only a chemical descaling of the metal strip, but alsoa mechanical ablation of the scale layer.

In the method, the metal strip is preferably transported parallel to itslength direction by a strip conveying device, especially by theaforementioned strip conveying device of the descaling device.

Preferably, the pickling agent which is sprayed onto the metal strip isor contains an acid, such as hydrochloric acid. The metal strip may bein particular a steel strip. Moreover, the metal strip is preferably ahot rolled metal strip.

In one advantageous embodiment of the invention, a pickling agentdispersing rate of the first outer spraying unit and a pickling agentdispersing rate of the second outer spraying unit of the at least onefirst spraying device and/or the at least one further spraying device isset by means of a control device each time at a value which is differentfrom a pickling agent dispersing rate of the respective middle sprayingunit of the first spraying device and the further spraying device. Inthis way, a homogeneous descaling result can be achieved especially inthe case when the scale has a different thickness at the edge regionsthan in the middle region.

For example, the pickling agent dispersing rate of the first outerspraying unit and the pickling agent dispersing rate of the second outerspraying unit may be set by means of the control device at a value whichis larger than the pickling agent dispersing rate of the middle sprayingunit, especially in the case of a larger thickness of the scale layer atthe two edge regions.

Basically, it is possible for the pickling agent dispersing rate of thefirst outer spraying unit and the pickling agent dispersing rate of thesecond outer spraying unit to be set by means of the control device atdifferent values. Thus, e.g., it is possible to set only the picklingagent dispersing rate of one of the two outer spraying units by means ofthe control device at a value which is different from the pickling agentdispersing rate of the middle spraying unit.

Advantageously, the pickling agent dispersing rate of the respectivespraying unit of the at least one first spraying device and/or the atleast one further spraying device is set with the aid of the controldevice such that the metal strip is acted upon in its width direction bythe first and/or the further spraying device with a given pickling agentspray profile. By the pickling agent spray profile is meant the profileof the pickling agent quantity applied by the spraying device to themetal strip along a given direction (here: the width direction of themetal strip).

The pickling agent spray profile may increase or decrease to the outsidein the first and/or in the second edge region, especially increase ordecrease in linear manner. Moreover, the spray profile may besymmetrical with respect to the strip center plane. By the strip centerplane is meant here a vertical plane relative to which the metal striphas a mirror symmetry.

Furthermore, the pickling agent spray profile with which the metal stripis acted upon may have no plateau. Alternatively, the pickling agentspray profile may have a plateau, especially between said two edgeregions.

A pickling agent spray profile of the aforementioned kind can berealized, e.g., in that the nozzles of the first outer spraying unit arearranged alongside each other in a triangle, the nozzles of the secondouter spraying unit are arranged alongside each other in a triangle andthe nozzles of the middle spraying unit are arranged alongside eachother in a trapezoid, especially in the form of an equilateraltrapezium, or likewise in a triangle.

The description given thus far of advantageous embodiments of theinvention contains numerous features which have been presented in theindividual dependent patent claims, sometimes assembled with several ofthem. However, these features may also be considered individually and beassembled into further meaningful combinations. In particular, thesefeatures may be combined individually and in any suitable combinationwith the descaling device according to the invention and the methodaccording to the invention. Moreover, method features may also be viewedas an attribute of the corresponding device unit.

Even if certain terms in the specification or in the patent claims areused in the singular or in connection with a numeral, the scope of theinvention shall not be limited for these terms to the singular or theparticular numeral.

The above described attributes, features and benefits of the invention,as well as the manner in which they are achieved, shall become moreclear and distinctly understandable in connection with the followingdescription of the exemplary embodiments of the invention, which shallbe discussed more closely in connection with the figures. The exemplaryembodiments serve for the explaining of the invention and do not limitthe invention to the combinations of features indicated therein, or inregard to functional features.

Moreover, suitable features of each exemplary embodiment may also beconsidered explicitly in isolation, removed from an exemplaryembodiment, introduced into another exemplary embodiment in order tosupplement it, and combined with any one of the claims.

If the same reference numbers are used in different figures, they denotesubstantially the same or equivalent elements. For reasons ofexpedience, however, substantially identical or equivalent elements mayalso be denoted with different reference numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary embodiment of a descaling device according to theinvention for chemical descaling of a metal strip;

FIG. 2 is a cross section through the descaling device of FIG. 1;

FIG. 3A is a representation of a first of two spraying devices of thedescaling device;

FIG. 3B is a representation of a second of the two spraying devices ofthe descaling device;

FIG. 4 is a pickling agent spray profile which is applied to the metalstrip in the descaling device;

FIG. 5A is a representation of a first of two other spraying devices fora descaling device;

FIG. 5B is a representation of a second of two other spraying devices ofthe descaling device; and

FIG. 6 is a pickling agent spray profile which is applied to a metalstrip when using one of the spraying devices of FIG. 5.

DESCRIPTION OF THE EMBODIMENTS

In the specification and claims “/” between two words or sets of wordsindicates one or the other is being named; “and/or” between two words orsets of words means either one or both.

FIG. 1 shows an exemplary embodiment of a descaling device 2 accordingto the invention for chemical descaling of a metal strip 4 in aschematic representation.

The descaling device 2 is outfitted with a strip conveying device 6 fortransporting the metal strip 4 along a conveying direction 8. In thepresent exemplary embodiment, the strip conveying device 6 is designedas a roller conveyor with multiple rollers 10.

Moreover, the descaling device 2 comprises multiple first or upperspraying devices 12 for spraying a pickling agent 14 containinghydrochloric acid onto a top side 16 of the metal strip 4 and multiplesecond or lower spraying devices 12 for spraying the pickling agent 14onto a bottom side 18 of the metal strip 4. In FIG. 1, as an example,four upper spraying devices 12 and four lower spraying devices 12 areshown. In theory, the descaling device 2 may also have a higher or lowernumber of such spraying devices 12.

The upper spraying devices 12 are arranged in succession in theconveying direction 8 of the strip conveying device 6. Likewise, thelower spraying devices 12 are arranged in succession in the conveyingdirection 8 of the strip conveying device 6. Moreover, the sprayingdevices 12 are each configured as a spray bar.

In the present exemplary embodiment, all the upper spraying devices 12of the descaling device 2 are arranged at the same height. All the upperspraying devices 12 of the descaling device 2 have the same distance tothe top side 16 of the metal strip 4. Moreover, all the lower sprayingdevices 12 of the descaling device 2 are arranged at the same height.All the lower spraying devices 12 of the descaling device 2 have thesame distance to the bottom side 18 of the metal strip 4.

The distance of the upper spraying devices 12 from the top side 16 ofthe metal strip 4 may be less than or greater than the distance of thelower spraying devices 12 from the bottom side 18 of the metal strip 4.Alternatively, these two distances may be equal. It is especiallypreferable when the distance of the lower spraying devices 12 from thebottom side 18 of the metal strip 4 is smaller than the distance of theupper spraying devices 12 from the top side 16 of the metal strip 4.

Some of the upper and lower spraying devices 12 may be spraying devices12 a of a first type. Some others of the upper and lower sprayingdevices 12 may be spraying devices 12 b of a second type. The sprayingdevices 12 a of the first type comprise a multitude of solid streamnozzles 20, whereas the spraying devices 12 b of the second typecomprise a multitude of slotted nozzles 22 (see FIGS. 3A and 3B).

In the present exemplary embodiment, the spraying devices 12 a of thefirst type and the spraying devices 12 b of the second type are arrangedalternating in the conveying direction 8 of the strip conveying device6. That is, a spraying device 12 a of the first type is followed in theconveying direction 6 by a spraying device 12 b of the second type,which in turn is followed in the conveying direction 8 by a sprayingdevice 12 a of the first type, and so forth. But, such alternation oftwo spraying devices next to each other is not required.

The spraying devices 12 b of the second type, i.e., the spraying devices12 b with slotted nozzles 22, are utilized in this embodiment inparticular to homogenize the descaling result.

However, the arrangement of the spraying devices 12 need not be such analternating one. Moreover, the same number of spraying devices 12 a ofthe first type and spraying devices 12 b of the second type need not bepresent. Furthermore, it is basically possible to use only sprayingdevices 12 of the same type in the descaling device 2.

Moreover, the descaling device 2 comprises a pickling chamber 24, inwhich said spraying devices 12 are arranged. The pickling chamber 24comprises a lower chamber portion 26 to receive the pickling agent 14draining from the metal strip 4 and an upper chamber portion 28 arrangedabove the lower chamber portion 26.

Furthermore, the descaling device 2 comprises a first squeezing rollerpair 30 and a second squeezing roller pair 32 each having an uppersqueezing roller 34 and a lower squeezing roller 36. The first squeezingroller pair 30 is arranged in front of the pickling chamber 24 in termsof the conveying direction 8, while the second squeezing roller pair 32is arranged in the pickling chamber 24. The squeezing rollers 34, 36support and guide the metal strip 4. In moving through a squeezingroller pair 30, 32, a liquid present on the metal strip surface isexpelled by the squeezing rollers 34, 36.

Furthermore, the descaling device 2 comprises a control device 38, ofwhich FIG. 1 shows its control unit 40, its first sensor unit 42 a andits second sensor unit 42 b.

Said sensor units 42 a, 42 b are connected to the control unit 40 andeach comprise an upper sensor row 44 and a lower sensor row 46. Thesensor rows 44, 46 of the first sensor unit 42 a are arranged in frontof or preceding the spraying devices 12 in regard to the conveyingdirection 8 of the strip conveying device 6. The sensor rows 44, 46 ofthe second sensor unit 42 b are arranged behind or following thespraying devices 12 in regard to the conveying direction 8 of the stripconveying device 6. Preferably, the sensor rows 44, 46 of the respectivesensor unit 42 a, 42 b—as shown in FIG. 1—are arranged outside thepickling chamber 24.

The metal strip 4 is transported by the strip conveying device 6parallel to its length direction 48 through the descaling device 2. Inthe pickling chamber 24, the metal strip 4 has the pickling agent 14applied to it by the spraying devices 12 in order to chemically descalethe metal strip 4, in other words, to remove a scale layer located onthe metal strip 4.

The upper sensor row 44 of the first sensor unit 42 a detects, in frontof or preceding the spraying devices 12 and resolved in location acrossthe width of the metal strip 4, a surface parameter of the metal strip 4which is dependent on the thickness of the scale layer on the top side16 of the metal strip 4. Accordingly, the lower sensor row 46 of thefirst sensor unit 42 a detects, preceding or in front of the sprayingdevices 12 and resolved in location across the width of the metal strip4, a surface parameter of the metal strip 4 which is dependent on thethickness of the scale layer on the bottom side 18 of the metal strip 4.

The upper sensor row 44 of the second sensor unit 42 b likewise detects,after or following behind the spraying devices 12 and resolved inlocation across the width of the metal strip 4, a surface parameter ofthe metal strip 4 which is dependent on the thickness of the scale layeron the top side 16 of the metal strip 4. Accordingly, the lower sensorrow 46 of the second sensor unit 42 b detects, after or following behindthe spraying devices 12 and resolved in location across the width of themetal strip 4, a surface parameter of the metal strip 4 which isdependent on the thickness of the scale layer on the bottom side 18 ofthe metal strip 4. The sensor rows 44, 46 of the second sensor unit 42 bmay in particular detect each time the same surface parameter as thesensor rows 44, 46 of the first sensor unit 42 a.

The sensor signals generated by the sensor rows 44, 46 of the sensorunits 42 a, 42 b are relayed to the control unit 40.

With the help of the control unit 40, the pickling agent application onthe metal strip 4 is controlled in dependence on the aforementionedsensor signals so that the most homogeneous possible descaling result isachieved, preferably with complete removal of the scale layer.

Basically, it is possible for the descaling device 2 to have only one ofthe two sensor units 42 a, 42 b, instead of both sensor units 42 a, 42b, and to control accordingly the pickling agent application on themetal strip 4 in dependence on the sensor signals of only one of thesensor units 42 a, 42 b.

The descaling device 2 can moreover have one or more dip tanks (notshown) for a dip pickling treatment of the metal strip 4. For example,the descaling device 2 may have one dip tank before the pickling chamber24 and a further dip tank after the pickling chamber 24. In therespective dip tank, the same pickling agent may be used as is sprayedby the spraying devices 12 onto the metal strip 4, or a differentpickling agent may be used.

FIG. 2 shows a cross section through the descaling device 2 along thesectioning plane II-II of FIG. 1.

Referring to FIG. 2, the configuration of the spraying devices 12 shallnow be described more closely.

As already mentioned, the spraying devices 12 are each configured as aspray bar.

The upper spraying devices 12 each comprise a first outer spraying unit50 for spraying the pickling agent 14 onto a first edge region 52 of thetop side 16 of the metal strip 4, a second outer spraying unit 54 forspraying the pickling agent 14 onto a second edge region 56 of the topside 16 of the metal strip 4, situated opposite the first edge region52, and a middle spraying unit 58, arranged between the two outerspraying units 50, 54, for spraying the pickling agent 14 onto a middleregion 60 of the top side 16 of the metal strip 4 situated between theedge regions 52, 56.

Accordingly, the lower spraying devices 12 each comprise a first outerspraying unit 50 for spraying the pickling agent 14 onto a first edgeregion 52 of the bottom side 18 of the metal strip 4, a second outerspraying unit 54 for spraying the pickling agent 14 onto a second edgeregion 56 of the bottom side 18 of the metal strip 4, situated oppositethe first edge region 52, and a middle spraying unit 58, arrangedbetween the two outer spraying units 50, 54, for spraying the picklingagent 14 onto a middle region 60 of the bottom side 18 of the metalstrip 4 situated between the edge regions 52, 56.

Said spraying units 50, 54, 58 of the respective spraying device 12 arearranged in succession in the width direction 62 of the metal strip 4.Moreover, each of the spraying units 50, 54, 58 comprises multiplenozzles 20, 22 (see FIG. 3).

Furthermore, the spraying units 50, 54, 58 are designed to spray thepickling agent 14 perpendicularly onto the top side 16 or bottom side 18of the metal strip 4. The nozzles 20, 22 of the spraying units 50, 54,58 are oriented such that the spraying units 50, 54, 58 each have aspraying direction 64 which is directed perpendicular to the top side 16or bottom side 18 of the metal strip 4, i.e., vertically upward orvertically downward.

The distance of the spraying devices 12 from the strip surface, or moreproperly the distance of their nozzles 20, 22 from the strip surface,may be as much as 500 mm in the present example.

Furthermore, each of the spraying units 50, 54, 58 has its own picklingagent distribution chamber 66, to which the nozzles 20, 22 of therespective spraying units 50, 54, 58 are each connected by theirinlet-side nozzle end.

Moreover, the descaling device 2 comprises a pickling agent supply line68 for each of the spraying units 50, 54, 58. The respective picklingagent supply line 68 empties into the respective spraying unit 50, 54,58 perpendicular to its spraying direction 64, so that a uniformpressure distribution is achieved in the individual spraying units 50,54, 58.

Furthermore, the aforementioned control device 38 comprises multiplepickling agent delivery pumps 70, in the present exemplary embodimentthere being provided a separate pickling agent delivery pump 70 for eachof the spraying units 50, 54, 58 (see FIG. 3). Each of the sprayingunits 50, 54, 58 is connected at the inlet side to the correspondingpickling agent delivery pump 70 across the pickling agent supply line 68connected to it. Basically, it is possible to supply spraying units 50,54, 58 of different spraying devices 12 with pickling agent 14 across acommon pickling agent delivery pump 70. In this case, the descalingdevice may comprise for example a total of three pickling agent deliverypumps 70 for all spraying devices 12 taken together.

Said pickling agent delivery pumps 70 are moreover each connected to theaforementioned control unit 40 of the control device 38, which isdesigned to use a given control algorithm to control the pickling agentvolume flow of the pickling agent delivery pumps 70.

The control device 38 is designed to set the pickling agent dispersingrate of the respective spraying units 50, 54, 58, and this independentlyof the pickling agent dispersing rates of the other spraying units 50,54, 58. By a change in the pickling agent volume flow of one of thepickling agent delivery pumps 70, the control unit 40 can change thepickling agent dispersing rate of the corresponding spraying unit 50,54, 58.

Preferably, the sum of the pickling agent dispersing rates of the threespraying units 50, 54, 58 of the respective spraying device 12 lies inthe range of 100 to 150 m³/h.

As mentioned above, the pickling agent application on the metal strip 4is controlled in dependence on the previously mentioned sensor signalsof the sensor units 42 a, 42 b such that the most homogeneous possibledescaling result is achieved.

If the thickness of the scale layer in the middle region 60 of the metalstrip 4 is less than that on the edge regions 52, 56 of the metal strip4, the pickling agent dispersing rate of its first outer spraying unit50 and the pickling agent dispersing rate of its second outer sprayingunit 54 in the respective spraying device 12 will be set by the controldevice 38 respectively at a value which is greater than the picklingagent dispersing rate of its middle spraying unit 58. On the other hand,if the thickness of the scale layer in the middle region 60 of the metalstrip 4 is greater than that on the edge regions 52, 56 of the metalstrip 4, the pickling agent dispersing rate of its first outer sprayingunit 50 and the pickling agent dispersing rate of its second outerspraying unit 54 in the respective spraying device 12 will be set by thecontrol device 38 respectively at a value which is smaller than thepickling agent dispersing rate of its middle spraying unit 58.

If the thickness of the scale layer is symmetrical with respect to avertical strip center plane, the pickling agent dispersing rate of itsfirst outer spraying unit 50 and the pickling agent dispersing rate ofits second outer spraying unit 54 in the respective spraying device 12will be set by the control device 38 at the same value.

In the event of a production-related decrease in the delivery speed ofthe metal strip 4, one or more spraying units 50, 54, 58 of the sprayingdevices 12 can be switched off to avoid an overpickling of the metalstrip 4.

FIG. 3A shows a spraying device 12 a of the first type and FIG. 3B showsa spraying device 12 b of the second type of the descaling device 2,each from their side facing toward the metal strip 4.

In FIG. 3A the aforementioned solid stream nozzles 20 of the sprayingdevice 12 a of the first type and in FIG. 3B, the aforementioned slottednozzles 22 of the spraying device 12 b of the second type can be seen.

Moreover, the already mentioned pickling agent delivery pumps 70 and thepickling agent supply lines 68 connected to the spraying units 50, 54,58 are represented in FIGS. 3A and 3B.

In the spraying device 12 a of the first type in FIG. 3A, the solidstream nozzles 20 are arranged in multiple nozzle rows orientedperpendicular to the conveying direction 8, these nozzle rows beingarranged equidistant from each other. In the respective nozzle row, thesolid stream nozzles 20 are likewise arranged equidistant from eachother.

The distance between adjacent solid stream nozzles 20 from the samenozzle row may correspond in particular to the distance between adjacentnozzle rows. This distance may amount to 25 mm, for example. At theirexit opening, the solid stream nozzles 20 preferably have an innerdiameter of 4 mm.

Moreover, the solid stream nozzles 20 of one nozzle row are arrangedwith an offset with respect to the row length direction from the solidstream nozzles 20 of the adjacent nozzle row, in order to avoid theformation of a striped spray pattern on the metal strip 4.

In the spraying device 12 b of the second type in FIG. 3B, each of itsspraying units 50, 54, 58 has slotted nozzles 22 of different width,which are arranged equidistant in succession in the conveying direction8 of the strip conveying device 6, the slotted nozzles 22 each beingoriented perpendicular to the conveying direction 8.

In both the spraying device 12 a of the first type in FIG. 3A and in thespraying device 12 b of the second type in FIG. 3B, the pickling agentdistribution chambers 66 of the two outer spraying units 50, 54 have atriangular cross section form, while the middle spraying unit 58 has across section form which corresponds to an equilateral trapezium. Thearrangement of the solid stream nozzles 20 and the width of the slottednozzles 22 is adapted to the cross section form in the respectivespraying unit 50, 54, 58.

In both the spraying device 12 a of the first type and in the sprayingdevice 12 b of the second type, the pickling agent distribution chambers66 are separated from each other by partition walls, which are indicatedin FIG. 3 by dashed lines.

Alternatively or additionally, for one or more of the spraying devices12 a, 12 b of the first or second type the descaling device 2 may have aspraying device not divided into three spraying units whose picklingagent dispersing rates are adjustable independently of each other, butinstead has only a single spraying unit. Such a spraying device may haveslotted nozzles, for example, which extend substantially across theentire width of the spraying device.

FIG. 4 shows a pickling agent spray profile which is applied to themetal strip 4 by one of the spraying devices 12 a of the first type orone of the spraying devices 12 b of the second type, in the form of adiagram.

In the diagram, the quantity of pickling agent V sprayed by the sprayingdevice 12 a, 12 b onto the metal strip 4 is represented as a solid lineas a function of a length coordinate x in the width direction 62 of themetal strip 4. The value b of the abscissa length coordinate xcorresponds to the width of the metal strip 4.

The contribution of the two outer spraying units 50, 54 to the picklingagent spray profile is represented in the diagram respectively by meansof a dashed line, whereas the contribution of the middle spraying unit58 is represented by a dotted line.

The pickling agent spray profile shown has a mirror symmetry. In themiddle region 60 of the metal strip 4, the pickling agent spray profilehas a plateau 72. In the middle region 60 the pickling agent sprayprofile does not change with the length coordinate x. In the first andin the second edge region 52, 56 of the metal strip 4, however, thepickling agent spray profile increases toward the outside (starting fromthe plateau 72).

FIG. 5A shows a spraying device 12 c of a third type and FIG. 5B shows aspraying device 12 d of a fourth type.

These two spraying devices 12 c, 12 d may be used in the descalingdevice 2 of FIG. 1 alternatively or additionally to one or more of thepreviously described spraying devices 12 a, 12 b.

The spraying device 12 c of the third type, like the spraying device 12a of the first type, comprises a multitude of solid stream nozzles 20,whereas the spraying device 12 d of the fourth type, like the sprayingdevice 12 b of the second type, comprises a multitude of slotted nozzles22.

The spraying devices 12 c, 12 d of the third and fourth type in FIGS. 3Aand 3B differ from the two spraying devices 12 a, 12 b of the first andsecond type in FIGS. 5A and 5B in that the pickling agent distributionchambers 66 of the two outer spraying units 50, 54 and the picklingagent distribution chamber 66 of the middle spraying unit 58 in thespraying device 12 c of the third type in FIG. 5A and the sprayingdevice 12 d of the fourth type in FIG. 5B respectively have a triangularcross section form.

Moreover, in the embodiments of FIGS. 5A and 5B valves 74 are providedto control the pickling agent dispersing rate of the respective sprayingunit 50, 54, 58 instead of pickling agent delivery pumps. In the presentexample, the valves 74 are each arranged in one of the pickling agentsupply lines 68. The valves 74 may be controlled by a control unit suchas the control unit 40 of the descaling device 2 of FIG. 1. Basically,it is possible to use valves and pickling agent delivery pumps incombination to control the pickling agent dispersing rate of therespective spraying unit 50, 54, 58.

FIG. 6 shows a pickling agent spray profile which is applied to a metalstrip 4 when one of the two spraying devices 12 c, 12 d of FIGS. 5A and5B is used for the pickling agent application on the metal strip 4.

This pickling agent spray profile differs from the pickling agent sprayprofile of FIG. 4 in that it has no plateau in the middle region 60 ofthe metal strip 4. Instead, the pickling agent spray profile of FIG. 6increases outwardly from the strip middle.

The pickling agent spray profiles represented in the diagrams of FIG. 4and FIG. 6 are exemplary pickling agent spray profiles. In each of thesetwo diagrams, the area enclosed by the two dashed lines and the dottedline respectively with the abscissa represents for example a regulatingrange of the corresponding spraying unit 50, 54, 58. Depending on theadjusted pickling agent dispersing rate of the respective spraying unit50, 54, 58, the quantity of pickling agent V sprayed onto the metalstrip 4 may take on other values in the first edge region 52, in themiddle region 60 and/or in the second edge region 56.

Although the invention has been illustrated and described more closelyin detail by the preferred exemplary embodiments, the invention is notlimited by the examples disclosed and other variations may be derivedfrom it, without leaving the scope of protection of the invention.

LIST OF REFERENCE NUMBERS

-   2 Descaling device-   4 Metal strip-   6 Strip conveying device-   8 Conveying direction-   10 Roller-   12 Spraying device-   12 a Spraying device of first type-   12 b Spraying device of second type-   12 c Spraying device of third type-   12 d Spraying device of fourth type-   14 Pickling agent-   16 Top side-   18 Bottom side-   20 Solid-stream nozzle-   22 Slotted nozzle-   24 Pickling chamber-   26 Chamber portion-   28 Chamber portion-   30 Squeezing roller pair-   32 Squeezing roller pair-   34 Squeezing roller-   36 Squeezing roller-   38 Control device-   40 Control unit-   42 a Sensor unit-   42 b Sensor unit-   44 Sensor row-   46 Sensor row-   48 Length direction-   50 Spraying unit-   52 Edge region-   54 Spraying unit-   56 Edge region-   58 Spraying unit-   60 Middle region-   62 Width direction-   64 Spraying direction-   66 Pickling agent distribution chamber-   68 Pickling agent supply line-   70 Pickling agent delivery pump-   72 Plateau-   74 Valve

1. A descaling device for chemical descaling of a metal strip, whereinthe metal strip passes through the descaling device; the metal striphaving a first edge region and a second edge region extending inwardlyfrom respective lateral edges of the metal strip passing through thedescaling device; the metal strip having a middle region situatedbetween the first and the second edge regions of the metal strip; themetal strip having a top side and a bottom side; the descaling device,comprising: at least one first spraying device and at least one secondspraying device for respectively spraying a pickling agent onto a topside/bottom side of the metal strip; each of the first spraying deviceand the second spraying device comprises a respective first outerspraying unit for spraying the pickling agent onto the first edge regionof the top side/bottom side of the metal strip and a second outerspraying unit for spraying the pickling agent onto the second edgeregion of the top side/bottom side of the metal strip, wherein thesecond edge region of the metal strip is situated opposite the firstedge region of the metal strip and extending inwardly from therespective lateral edges of the metal strip; and the first sprayingdevice further comprises a middle spraying unit for spraying thepickling agent onto a middle region of the top side/bottom side of themetal strip, the middle region is between the first and the second edgeregions; at least one of the spraying units of the first/second sprayingdevice comprises multiple rows of solid stream nozzles; each of thespraying units of the first/second spraying device comprises its ownrespective pickling agent distribution chamber; at least one of the twoouter spraying units of the second spraying device comprises at leastone slotted nozzle; and each of the two outer spraying units (50, 54) ofthe first and second spraying device devices comprises its ownrespective pickling agent distribution chamber.
 2. The descaling deviceas claimed in claim 1, further comprising the at least one secondspraying device comprises a middle spraying unit situated between theend regions for spraying the pickling agent onto a middle region of thetop side/bottom side of the metal strip; wherein the middle sprayingunit of the second spraying device comprises at least one of the slottednozzles and comprises its own pickling agent distribution chamber. 3.The descaling device as claimed in claim 1, wherein each of the sprayingdevices comprises a spray bar.
 4. The descaling device as claimed inclaim 1, further comprising a control device configured for adjusting apickling agent dispersing rate of each respective spraying unit of eachof the spraying devices.
 5. The descaling device as claimed in claim 4,further comprising the control device being operable for adjusting thepickling agent dispersing rate of the middle spraying unit independentlyof the pickling agent dispersing rate of the first outer spraying unitand independently of the pickling agent dispersing rate of the secondouter spraying unit.
 6. The descaling device as claimed in claim 4further comprising the control device comprises multiple pickling agentdelivery pumps configured for adjusting the pickling agent dispersingrates of the spraying units, wherein the pickling agent delivery pumpshave an exit side connected to the respective ones of spraying device.7. The descaling device as claimed in claim 4, further comprising thecontrol device comprises multiple valves configured for adjusting thepickling agent dispersing rates of the spraying units, wherein eachspraying device is connected at an entry side of the spraying device tothe valves.
 8. The descaling device as claimed in claim 4, furthercomprising the control device comprises a sensor unit having at leastone sensor for detecting a surface parameter of the metal strip, and thecontrol device is configured to adjust the pickling agent dispersingrate of the respective spraying unit in dependence on an output signalof the sensor unit.
 9. A method for chemical descaling of a metal strip,comprising: spraying a pickling agent onto a top side/bottom side of themetal strip by at least one first spraying device onto the top side ofthe strip and by at least one second spraying device onto the bottomside of the strip; wherein the spraying of the pickling agent is by afirst outer spraying unit of the first spraying device, and by a firstouter spraying unit of the second spraying device onto a first edgeregion of the top side/bottom side of the metal strip; and the sprayingof the pickling agent is also by a second outer spraying unit of thefirst spraying device and by a second outer spraying unit of the secondspraying device onto a second edge region of the top side/bottom side ofthe metal strip wherein the second edge region is situated opposite thefirst edge region and, both of the first and the second edge regionextending inwardly from respective lateral edges of the metal strip; andthe spraying of the pickling agent is also by a middle spraying unit ofthe first spraying device onto a middle region of the top side/bottomside of the metal strip, wherein the middle region is situated betweenthe first and second edge regions of the metal strip; the spraying ofthe pickling agent onto the top side/bottom side of the metal strip isby at least one of the spraying units of the first spraying devicethrough multiple rows of solid stream nozzles; and by the spraying by atleast one of the two outer spraying units of the further spraying devicethrough one or more slotted nozzles.
 10. The method as claimed in claim9, further comprising: spraying the pickling agent onto a middle regionof the top side/bottom side of the metal strip, the middle region issituated between the first and second edge regions, of the metal strip,the spraying being through at least one slotted nozzle of a middlespraying unit of the at least one second spraying device.
 11. The methodas claimed in claim 10, further comprising: setting a pickling agentdispersing rate of the first outer spraying unit and a pickling agentdispersing rate of the second outer spraying unit of the at least onefirst spraying device and/or of the at least one second spraying device,wherein the dispersing rate is set by a control device each time at avalue which is different from a pickling agent dispersing rate of therespective middle spraying unit of the first spraying device and of thesecond spraying device.
 12. The method as claimed in claim 11, furthercomprising: setting the pickling agent dispersing rate of the respectivespraying unit of the at least one first spraying device and/or of the atleast one second spraying device with the aid of the control device foracting upon the metal strip in a width direction of the strip by thefirst spraying device and/or by the second spraying device with a givenpickling agent spray profile, wherein the pickling agent spray profileincreases or decreases to a respective lateral outside of the metalstrip in the first and/or in the second edge region.
 13. The method asclaimed in claim 12, wherein the pickling agent spray profile has noplateau.
 14. The method as claimed in claim 12, wherein the picklingagent spray profile has a plateau between the two edge regions.
 15. Thedescaling device of claim 8, wherein the surface parameter of the metalstrip is dependent on the thickness of the scale layer of the metalstrip.